Electrodeposition of tungsten alloys



Patented May 30,1939

l-QUNlTEDY STAT nmc'raonnrosrrion or TUNGSTEN ALLOYS 4 vHarry HowardArmstrong and Arthur Burley Menefee, Beverly Hills, Galif., asslgnors toI Tungsten Electrodeposit Corporation, Washington, D. (3., a corporationof Delaware 1 o p Serial No. 28,187

" No Drawing. Application June 24, 1935,

19 Claims.

This invention relates to the electrodeposition. of tungsten alloys ofvariable tungsten content The present invention is part-acontinuatlonofprior application Serial No. 14,372, filed April 2, 1935.The wide potential utility of the heavier refractory metals, such asthose of the 5th and 6th groups, has long been recognized\ andconsiderable effort has been expended in attempting to electrodepositsuch metals. Particularly valul5 able among such metals are tungsten andtantalum. These are each characterized by a very high resistance tochemical corrosion and are r most refractory; furthermore they presentdecidedly pleasing chromatic characteristics. Such 2o metals eitheralone or in the form of alloys pre- Consonant with the recognition ofthe inherent value of these metals in the several technological fieldsmany suggestions have been. advanced as I, to methodsofelectrodepositing them. It has been proposed, for example, to producepure tantalum by electrodeposition. This is, and has been, recognized asdifficult' of achievement becauseof the fact that compounds of tantalumhydrolyze relatively readily in water,-giving rise to the formation ofinsoluble or very sparingly soluble salts. To evade this difliculty ithas been proposed toplate tantalum from a non-aqueous or anhydrous bath.Thus it has been suggested to dissolve a suitable tantalum, compound,such as tantalum chloride, in an organic solvent, such as toluene, toelectrodeposit pure tantalum from the resulting solution. Similarly ithas been suggested to dissolve tantalum compounds in anhydrous liquidammonia and subsequently to electro-deposit tantalum from this solution.

ature required, the very low inherent conductivity and the high solutionresistivity of such organic baths. In some circumstances thesedifllculties All such methods involving the utilization of 55 arefurther accentuated by the. physical or mechanical difllculties, such inthe case of anhydrous ammonia, for example, as the problem of fretaining the ammonia in the liquid phase.

Similarly, as pointed out in our prior application'above referred to,comparable difllculties ob- 5 tain in the electrodepositionof tungsten.Thismetal is difflcult to electrodeposit because'of the tendency oftungsten to oxidize and deposit in the oxide condition, thus v givingrise to' impure and loosely adherent plates. By reason of the 10 Idifliculty of reducing oxides of tungsten in aqueous solution, duetoactive hydrolysis, it has been suggested to substitute an organicsolvent for the water bath. Such methods however present thedisadvantages enumerated above. 15

As fully disclosed in our copending application, we have found that itis not, only possible but is eminently feasible and practical to elec-'trodeposit tungsten containing alloys from aqueous baths. 1

We have now found that dense, lustrous. ad-

' herent alloy deposits containing tantalum may be obtained whenemploying aqueous baths. Improved results are secured, as will be seen,by codepositing other metals, such as tungsten and/or nickel, with thetantalum. When operating under the preferred conditions, smooth, evendeposits of extremely small crystalline struc-' ture are procurable.Without advancing any definite statement as to the precise mechanism ofthe reactions involved, it would appear that-ionic complexes are formedwhich present sumcient stability to resistthe tendency of the tantalum,tungsten, and comparable metallic ions, to hydrolyze to form insolubleoxidesor salts.

A major object of the present invention, therefore, is to electrodeposittantalum from aqueous electrolytes, s

Another object is to electrolytically produce alloys of tantalum. 40

Yet another object is to produce an aqueous electrolyte from whichtantalum may be electrolytically deposited.

A further object is to produce, as-a new article of manufacture, a metalbase plate having an adherent electrodeposit plate containing tungstenand tantalum.

Yet another objectof the invention is to elec- 3 trolytically producealloys of tungsten and tantalum of variable content ratios.

With these and other equally important and related objects in view,the'invention comprehends the concept of producing elec'trodeposited Wehave found that, similarly to tungsten,

. readily available compounds of tantalum, such as ll the oxides, may bedissolved in suitable aqueous solutions. We have further found thatwhen, to an electrolyte containing soluble tungsten and tantalum, thereis added another metal, such for example as nickel, the alloy plates ofthese metals,

duced. We have found in particular that such a common tantalum compoundas tantalum pentoxide (TazOa) may directly be .dissolved in a suitableaqueous solution, such as a solution ,of

ammonium acid fluoride (NaH4HFz). As has been disclosed in our priorapplication, common tungsten compounds, such as the oxides and tungsticacid anhydride, are likewise directly soluble-in ammonium acid fluoride.We have also :0 further found that such compounds are soluble within arelatively wide range and thus, by reason of the common solubility ofcompounds of the two metals in a single cheap aqueous solvent,

a most economic method of electrolytically proll ducing alloys of themetals is presented. The

advantages of the employment of simple, cheap.

and readily controllable aqueous, baths over the organic solventsheretofore suggested will immediately recommend themselves to thoseskilled so in the art.

As will appear more fully hereinafter, the bath of the present inventionmay be considerably modified with respect to such factors as thespecific amounts of the respective metals dissolved in the bath, theacidconcentration, temperature and current density ranges, the characterof the buffers and addition agents and the like. Similarly the anodesemployed may be of the inert type or may comprise one or more. of themetals which are to be deposited, it being particularly understood thatthe invention comprehends the establishment of the desired metal ions inthe bath by direct dissolution or anodic corrosion.

The invention will be more readily understood composition of typicalelectrolytes and the operative procedure.

proved bath from which an alloy plate may be deposited may be made up bysimultaneously or.

sequentially dissolving tungstic acid, tantalum pentoxide and ammoniumbifluoride in water while maintaining the water at a temperature oftween approximately 106 F. and 210 F. Thus, to, say oneliter of watermaintained at the temperature stated,there is added approximately 85grams of ammonium bifluoride, 40 grams of tungstic acid and grams oftantalum pentoxide.

After complete dissolution the solution is flltered and then there isadded 60 grams of tartaric acid, 30 grams of citric acid, 60 grams ofsodium fluorideand15-grams of a soluble nickel salt, such as nickelchloride. The solution is then adjusted to a pH of approximately 5.3using sodium hyof widely varient ratios, may eiliciently be pro-- solvedin 500 cc. of water.

from a consideration of the compounding and As a typical example an im-During the the bath. For example, an improved bath may be made up bydissolving 40 grams of tungstic acid, grams of ammoniiun bifluoride and30 grams of tartaric acid in 500cc. of water maintained'at elevatedtemperature for a period of time sufliciently prolonged to insurecomple'te dissolution. There is then separately prepared a 80-- lutionof 35 grams of tantalum pentoxide, 40'

grams of ammonium acid fluoride, 30 grams or tartaric acid and 20 gramsof nickel chloride dis This second batch was similarly heated to atemperature of the order of 160 F. until complete dissolution waseffected; The two solutions were then mixed and '75 cc. of sodiumhydroxide added. Upon electrolyzing, using brass, copper, steel or othersuitable cathode and tungsten carbide and/or nickel anodes, dense acidresistant plates were produced.

This type of bath may be considerably modifled with respect to the acidconcentration. Thus to the above *described bath there was added an vadditional quantity in the amount of cc. of

sodium hydroxide and the bath electrolyzed, using a steel cathode andfour tungsten carbide anodes. The bath temperature was maintained at 160F. and an 8 sq. in. test plate was plated for fifteen minutes at 4 amps.and 3 volts. Upon analysis this plate was found to contain 25.8%tantalum,\39.8%"tungsten and-34.4% nickel.

As will be appreciated and as indicated above, the nickel or tungstencontent of the bath may be replenished. either by using tungstencontaining and/or nickel containing anodes and producing the tungstenand nickel ions respectively by anodic corrosion. Similarly, if desired,replenish- '35 ment of the bath may be achieved by dissolvinga tungstenoxide or tungstic acid separately in ammonium acid fluoride and addingthis in re quired amounts. The tantalum content is most readilyreplenished by making a replenishing solution comprising tantalumpentoxide dissolved in a solution containing ammonium bifluoride and anorganic acid, such as tartaric.

Similarly in other experiments conducted it was found that tartaric acidmay be replaced in whole or in part by equivalent amounts of citricand/or boric acid. These acids appear to function to preventprecipitation of the tungsten and tantalum from the bath. Sodiumtartrate likewise has been found to be a useful and effective adjuvant.

It is further found that additions of ammonium phosphate improve theefficiency of the bath and the character of the ultimate plate.

As a result of considerable experimentation we have found that the platemay be produced over a'- wide pH range extending from a very acid to adefinitely alkaline solution. This should be ad- 'justed to secure thedesired results. Similarly the modification of the other factors, suchas the current density, has a marked effect upon the character of theplate. Thus on plating an 8 sq. in.

test plateat 2 amps. a bright plate is produced which may be buffed to avery brilliant flnish. With the same bath and size test plate, platingat 4 amps. produces a less brilliant but more acid resistant plate.Again, when carrying out the plating at 8-amps. a plate is producedwhich is extremely hard to buff and which when buifed is not asbrilliant as the plates described, but which is characterized by anextremely high resistance resistance of the plate applies generallywhatever the character of the work or base plate.

We have found that the respective quantities ,to acid. This variation inthe brilliancy and acid 1 metals in the bath. Furthermore theproportions of the several metals inthe plate may be varied 175, anadherent acid resistant plate is pmduring a given continuous platingoperation by duced.

changin the current density and/or the tem- In commercial operationsabath concentrate perature. It will be appreciated that the exmay bemade up in the dry or liquid condition.v amples given aboveare presentedas illustrative Thus a standardized liquid concentrate may be of theprocess and not as the exclusive methods made up, as will beappreciated, by dissolving 10 of either making up the bath or effectingthe predetermined quantities of'a tantalum and tung- Y platingoperation. Thus plates of the charsten compound in ammonium bifluorideand addacter described may be produced operating at pH ing to this therequired mounts of "organic ranges from 1 to 8 or more. Likewise currentacids, such as tartaric or citric, to maintain the density may be variedwith good results from submetals in solution. Thus for subsequent usethis 15 stantlally 6 to 500 or more amps. per sq. ft. of bath maybediluted with water andadditional submerged cathode area. Also, while anoptimum metal, such as nickel, by way of the soluble nickel temperatureof 150 to 160 F. has been desalt, and the bath electrolyzed by aninertanode scribed, it is, to be. understood that this temperatungstencarbide and/or nickel or other metal ture may be varied over a range offrom 80 F. containing anodes. p 20 or less to 180 F. or more. It will beappreciated that the'invention is not.

A striking, feature of the present invention is limited to the use ofthe particular tantalum comthe non-critical nature or flexibility ofthe'procpounds mentioned or to the described method of ess, especiallywith respect tothe solution concenbringing tantalum into 501M101! b fl ptrations. Thus, employing the method described, hends any method bywhich the tantalum is made 25 ,namely by utilizing an ammoniumbifluoride to available in an aqueous system. Thus improved solubilizethe tungsten and tantalum a very high results are procuredv bydissolving freshly preconcentration of these metals may be obtainedpared tantalum hydroxide in tartaric acid and in the bath. Forexample .atungsten concentraadding this solution to a solution of a tungsten tionof up to 6 oz; per gal. of bath solution can compound in abifluoride,and utilizingthe resultbe obtained by dissolving tungstic acid ortungstic ing solution after adjustment ofthe acid conacid anhydride in abifluoride solution. centration as'the plating bath.

The invention is not limited to the employment While the invention hasbeen described with of ammonium bifluoride. In lieu of this otherrespect to plating out the nickel alloys on common similarly actingbifiuorides, such as those, .-demetals, such .as steel, brass, copperand the like, 85

. scribed in the copending application referred to, it willbeappreciated that it is equally applicable maybe employed. Again, ifdesired, sodium acid for purposes of overplating on. more expensivefluoride maybe utilized to'bring the tungsten into metals, such asoverplating on an electrode: solution, as for example by dissolvingsodiumposited nickel plate.- Thus the invention is sustungstate inhydrogen fluoride and thereafter ceptible of widemodiflcations withrespect to the 0 adjusting the bath to the desired acidconcentraingredients employed and \their method of com- 1 tion. It willbe appreciated that-this process is pounding. The invention isconsidered to reside amenable to the general operative technique ofbroadly in the concept of'producing tantalum conthe plating art. Thus itis directly contemplated, taining electrodep'ositedplates from aqueousbaths when desired, to utilize addition agents, such as and also in theproduction of a highly serviceable heavy molecular weight colloids ofthecharacter electrodeposited tungsten tantalum surface. I of glue, forenhancing the quality of the'plate. We claim:

Likewise for certain types of work the bath may 1. A method of producingtantalum containing be subjected to very fine clarification to removeelectrodeposited plates which comprises electroundesired suspendedmatter, as for example by lyzing an aqueous acid solution of an alkalibim, treating the bath with aprecipitated colloid and fluoridecontaining dissolved tantalum and then filtering out the precipitatedmaterial. tungsten. i

It is particularly to beunderstood that the -.2. A method'of producingtantalumscontainprocess is not limited to the production of a ingelectrodeposited' plates which comprises elec-' ternary alloy or analloy containing nickel. Thus trolyzing an aqueous acid solution of analkali u in lieu of nickel chloride, other nickel salts maybifluoridecontaining dissolved tantalum and be utilized in the bath.Similarly in lieu of ,nickel; 4 nickel any other metal which forms anacid 3. A method of producingprotective electrodefluoride may beemployed, such for example as pbsited plates which compriseselectrolyzing an iron, nickel, cobalt and the like. aqueous solution ofan alkali bifluoride contain- '0 F 1 some p p 1' s a surface ombining'ing dissolved tantalum, tungsten and nickel. the decidedly refractorycharacteristics of tung- 4, A method of producing surfacescontainins'sten and tantalum is desirable. In these cirt t tantalum and nickelwhich comprises ,cu ances t e p es t e d is available for dissolvingtungsten containing and tantalum con h Production of a tungsten tantal mall y. taining compounds inahot aqifeous solution coni be produced byheating 20 grams of tantalum of the alloying components of the plate maybe maintain the tantalum in solution. when elecwidely varied, as forexample by adjusting the trolyzing the above solution, using a 4 sq. in.initial respective concentrations of the several copper cathode andtungsten carbide anode, at 9 amps. and 6 volts and maintaining the bathat taining an alkali bifluoride and citric acid; adjusting the hydrogenionconcentration of the solution to substantially pH 5.3 andelectrolyzing' the solution witha metal cathode and a tungstencontaining anode.

Thus, for example, a plate of this character may pentoxide, 60 grams oftungstic acid and grams of ammonium bifluoride and 65 grams of tartaricacid in approximately 800 cc. of water. This may be adiusted'to thedesired pH value, say a pH of 2.73. It has been found that in producinga tungsten and tantalum which comprises dissolv- 10 5. A method ofproducing surfaces containing resistant tungsten tantalum alloy thehigher acid ing a tantalum containing compound in an aqueconcentrationsare desirable, for at low acid conous solution of an alkali bifluoride,acidifying the centrations, of the order of pH. 6.2, it is dimcult tosolution, electrolyzing the solution with a tungsten containing anodeand coplating tungsten and tantalum upon a conductive cathode.

6. A method of producing surfaces containing tungsten and tantalum whichcomprises dissolving tungsten and tantalum containing compounds in anaqueous solution of an alkali bifluoride, acidifying the solution andelectrolyzing" the solution with a conductive cathode and a tungstencarbide anode.

7. A method of producing surfaces comprising tungsten tantalum andnickel which comprises dissolving tungsten, tantalum and nickelcontaining compounds in an aqueous solution of an alkali bifluoride,acidifying the solution, and electrolyzing the solution with aconductive cathode and tungsten containing and nickel containing anodes.

8. A method of producing tantalum containing surfaces which comprisesdissolving tungsten tantalum compoundsin an aqueous solutionof an alkalibifluoride, adjusting the hydrogen ion con-' centration of the solutionto between pH 1 and pH 8 and electrolyzing the solution with a metalcathode and a tungsten containing anode.

- 9. A method of producing adherent, acid re-' sistant tantalumcontaining electrodeposited plates which comprises dissolving tungstenand tantalum in an aqueous solution of an alkali biiluorlde, acidifyingthe solution, and electrolyzing the solution with a conductive cathodeand a tungsten containing anode, and increasing the amperage inproportion to the desired degree in acid resistance of theelectrodepositedplate' 10'. A method of producing tantalum containingsurfaces which comprises dissolving tungsten and tantalum containingcompounds in an aqueous solution of an alkali bifluoride, adding theretoan organic acid which acts to prevent the precipitation of,theidissolved metals from the solution; adjusting the hydrogen ionconcentration of the solution to between pH 1 and pH 8; ad-

justing'the temperature of the solution to between substantially F. andsubstantially F., electrolyzing the solution with a conductive cathodeand a metal anode, and varying the cur-- byreacting a tantalumcontaining compound. with an alkali bifluoride. and dissolving in thesolution a compound of a metal of a group consisting of tungsten, ironnickel and cobalt.

13. A method of producing tantalum-containing electrodeposited plateswhich comprises electrolyzing an aqueous acid solution of an alkalibirluoride containing dissolved tantalum and a metal of the groupconsisting of tungsten, iron, nickel and cobalt and an organic acid ofthe group consisting of citric acid and tartaric acid, said acids beingadapted to prevent precipitation of the metals from the solution.

14. An electroplating bath for electrodepositing tantalum comprising anaqueous solution formed by dissolving a tantalum containing compound anda compound of a metal coplatable with tantalum, said metal being chosenfrom the group consisting of tungsten, iron, nickel and cobalt,

in an aqueous acid solution of a bifluoride.

15 An electroplating bath for ele'ctrodepositing tantalum whichcomprises tantalum pentoxide and a tungsten containing compounddissolved in an aqueous solution of an alkali bifluoride, the bathcontaining a predetermined amount oi an organic acid .of the groupconsisting of tartaric and citric acids, adapted to preventprecipitation of the metals from the bath.

16. A method of producing tantalum containing'electrodeposited plateswhich comprises electrolyzingfla definitely acid aqueous'alkalibifluoride solution containing tantalum and tungsten ions. I

, 17. A method of producing tantalum containing-electrodeposited plateswhich comprises elec ftrolyzing an acid aqueous solution of 1 a fluoridecontaining dissolved tantalum, a metal coplatable with tantalum chosenfrom the group consisting of tungsten, iron, nickel and cobalt, and anorganic acid of the group consisting of tartaric and citric acid,adapted to prevent precipitation of the metals from the solution.

18. ,A method of producing tantalum containing alloys which comprisesdissolving an oxide of [tantalum in an alkali bifiuoride, adding anorganic acid of the group consisting of tartaric and citric acids,adjusting the hydrogen ion concentration to between pH 1 and pH 8,electrolyzing the solution and depositing tantalum on an electrode.

19. A method of protecting metals which com prises immersing the metalin an aqueous alkali bifluoride electrolyte containing" dissolved tan,-talum and tungsten, adjusting the acidity to between pH 2.7 and pH 6.2,electrolyzing the solution and plating out tungsten and tantalum on thesaid metal.

HARRY HOWARD ARMSTRON. ARTHUR BURLEY MENEFEE.

